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Abstract

We present correlated experimental and theoretical studies on the magnetic field modulation of Surface Plasmon Polaritons (SPPs) in Au/Co/Au trilayers. The trilayers were grown by sputter deposition on glass slides with the Co films placed at different distances from the surface and with different thickness. We show that it is possible to tailor Au/Co/Au trilayers with the critical thickness needed for optimum excitation of SPPs leading to large localized electromagnetic fields. The modification of the SPP wave vector by externally applied magnetic fields was investigated by measuring the magneto-optical activity in transverse configuration. In addition, using magneto-optics as a tool we determined the spatial distribution of the SPP generated electromagnetic fields within Au/Co/Au samples by analyzing the field-dependent optical response, demonstrating that it is possible to excite SPPs that exhibit large electromagnetic fields that are also magneto-optically active and therefore can be modulated by externally applied magnetic fields.

Figures (7)

(a) Schematic view of momentum matching in the Kretschmann configuration, where far-field radiation couples symmetric leaky SPP modes at the air-metal interface by means of a glass prism. Hy represents the only magnetic component in the TM mode. (b) Dispersion relation for such modes in Co and Au films considering their absorption losses. The dashed line shows the dispersion relation for Au considering no absorption losses. The dispersion relation of Co splits into two branches when external magnetic fields are applied along the y direction.

Schematic view of the SPP excitation in the Kretschmann configuration for the Au(3nm)/Co(dCo)/Au(dAu) trilayers where external magnetic field Hext is applied along y. (a) Reflectivity curves calculated for Co and Au films with critical thickness, (b) SPPs |Hy| at the metal-air interface for Co and Au films as a function of the thickness and (c) Transverse magneto-optical Kerr effect ΔR for a single Co film and for Au(3nm)/Co(dCo)/Au(20 nm) trilayers as a function of the Co thickness. The lower row represents calculations of (d) Rmin, (e) |Hy|max and (f) ΔRmax for any combination of Au and Co thickness in the Au(3nm)/Co(dCo)/Au(dAu) trilayers.

(a) Experimental and (b) simulated angular dependency of the reflectivity with no external magnetic field applied Rpp for the Au(3 nm)/Co(dCo)/Au(20 nm) trilayers with dCo ranging from 2.5 to 10 nm. (c) Real (n) and imaginary (k) parts of the complex refractive index of Co film measured with ellipsometry.

(a) Transverse magneto-optical Kerr effect ΔR=R(+H)-R(-H) measured in the Kretschmann configuration for the Au(3 nm)/Co(d)/Au (20 nm) trilayers with d ranging from 2.5 to 10 nm. (b) Field dependent variation of the SPP wave vector Δksp=ksp(+H)-ksp(-H). The dashed line represents the energy of the radiation used in the measurements E=1.96 eV.

Angular dependence of the relative variation in reflectivity ΔRpp/ Rpp for the Au(3 nm)/Co(d)/Au(20 nm) trilayers with d ranging from 2.5 to 10 nm. A maximum value of ΔRpp/ Rpp~3.2 (relative variation of 320%) is found for the trilayer with d=2.8 nm.

(Color online) Variation with the incidence angle of the reflectivity (left column) and MO response (right column) for the Au/Co/Au trilayers with Co positioned at 3 nm (up), 11.5 nm (middle) and 23 nm (down) to the upper air-Au interface using (a) p-polarized light, (b) light rotated 45° from the s (and p) axis and a polarization analyzer oriented at 45°, (c) same as (b) but inserting a quarter wave plate with its fast axis along p and (d) using s-polarized light.

(Color online) (a) Modulus of the product of the TM electric components ExEz normalized to the incident intensity at the position in which the ferromagnetic film is placed in each case for the Au/Co/Au trilayers with Co positioned at 3 nm (up), 11.5 nm (middle) and 23 nm (down) to the upper Au-air interface. The dashed line represents the estimated value of ExEz at the air-metal interface. (b) ExEz is represented as a function of incidence angle and distance to the upper Au-air interface.